Curable resin compositions are generally used in coatings, adhesives, and molding materials because of their thermal and mechanical properties. These curable resins are mainly composed of oligomers and monomers and their concrete examples are epoxy acrylates, urethane acrylates, ester acrylates, and unsaturated polyesters. Of these compounds, particularly the oligomeric components exert a great influence on the properties of the coating films to be formed after curing or those of the molded articles and, in consequence, the properties of the oligomeric components assume great importance for manifestation of good material performance. These compounds generally have a linear molecular structure and tend to increase in voscosity and become highly viscous as their molecular weight and content increase; thus it becomes necessary to use the monomeric component and, in some cases, an organic solvent in order to adjust the viscosity to an optimal level for usage.
The monomers used in this manner, however, have a low density of functional groups per molecule and lower the crosslinking density after curing and, furthermore, the residual monomers remaining unreacted in the coating film after curing degrade the mechanical and thermal properties of the film.
In addition, the use of monomeric components and organic solvents is a disadvantage during work on account of odor and, in particular, the use of organic solvents is not necessarily a desirable method for controlling the viscosity because of a growing tendency to avoid it from the standpoint of reducing the release of volatile components.
The use of liquid polyfunctional monomers is another approach to solve the aforementioned problems, but the effect which the monomers of this type produce for lowering the viscosity is no more pronounced than that of monomeric components and organic solvents and, furthermore, the polyfunctionality tends to cause the coating film to undergo large shrinkage after curing and has made it difficult to obtain satisfactory results in respect to the properties of coated films, particularly long-term reliability at high temperature and high humidity.
The present inventors have conducted extensive studies to solve such long outstanding problems, come across aromatic ester (meth)acrylate dendrimers which have a highly branched molecular chain containing terminal (meth)acrylate groups, found that the use of such dendrimers gives curable resin compositions which form cured films of excellent heat and moisture resistance, and completed this invention.
Accordingly, an object of this invention is to solve the aforementioned problems and provide novel aromatic ester (meth)acrylate dendrimers which are low in viscosity, highly curable, and capable of forming cured films of excellent heat and moisture resistance and curable resin compositions containing said dendrimers as essential component.